This is a classic Greek accompaniment, usually served with pita wedges or on the side with Greek dishes. We have our souvlaki without it, but just in case you prefer souvlaki with tzaziki (too fun to say), here's a recipe.
1 large cucumber, peeled and cut lengthwise, with seeds removed
3/4 cup plain yogurt
3/4 cup sour cream (OR use plain yogurt)
3 tablespoons olive oil
4 teaspoons fresh dill, minced (or a few shakes of dried dillweed)
4 1/2 teaspoons red wine vinegar
3 garlic cloves, minced
1/4 teaspoon salt
*This can be made without the dill entirely, or with mint substituted for the dill, to taste.
Grate the cucumber into a small bowl and squeeze between paper towels several times to remove excess moisture. Stir in remaining ingredients and blend well; if desired, blend in food processor. Refrigerate for a minimum of one hour and serve with pita wedges, etc.